SPEC 4.3.1.9 • DISCOVERY AND DEVELOPMENT OF DRUGS
Discovery & Development of Drugs
Three named drugs from plants and microorganisms. The modern three-stage testing process. Why double-blind trials matter. Lesson 3.06 · Paper 1 · Higher.
The Marks That Get Thrown Away
Spec 4.3.1.9 is short — but it loads up the paper with one-mark recall items: name the plant, name the property, name the stage. These are the cheapest marks on the paper.
Mark schemes for this topic reward the exact named term. Add irrelevant extra detail and the mark can be capped; substitute a near-synonym for a spec term and the mark is lost. Precision over fluency.
3
Named drugs you must know
3
Properties drugs are tested for
2
Testing phases (preclinical & clinical)
Why This Lesson
Spec 4.3.1.9 lists exact named examples and an exact testing sequence. Mark schemes reward the specific words. This lesson is a vocabulary lesson with a process attached. Learn the names; learn the order.
Learning Objectives
By the end of this lesson, you will be able to:
1
Name three traditional drugs and the plant or microorganism each one originates from.
2
Describe the stages of drug testing — preclinical, then clinical — using the correct named items at each stage.
3
Explain why placebos and double-blind trials are used — i.e. to remove bias.
Spec Anchor
AQA 8461 · Section 4.3.1.9 · Paper 1 · Higher Tier · Assesses AO1 (recall of named examples) and AO2 (application to unfamiliar drug-trial contexts).
Three Drugs You Must Name
The spec lists exactly three named examples of traditional drugs from plants and microorganisms. Memorise all three pairs — drug and source.
DrugSourceUse
DigitalisFoxgloves (a plant)Heart drug — used to treat heart conditions.
AspirinWillowPainkiller; also reduces fever.
PenicillinPenicillium mould (a microorganism)The first antibiotic — kills bacteria.
Spec wording check
The spec phrases it as: "The heart drug digitalis originates from foxgloves. The painkiller aspirin originates from willow. Penicillin was discovered by Alexander Fleming from the Penicillium mould." If asked, give the source the spec gives.
Penicillin — the Microorganism Example
Penicillin is the spec's example of a drug discovered through observation and accident.
Definition · Penicillin
Penicillin was discovered by Alexander Fleming from the Penicillium mould. It was the first antibiotic and works by killing bacteria.
Mark-Scheme Trip-Up
If a question asks who discovered penicillin → Fleming. If a question asks what it was discovered from → the Penicillium mould. Same lesson, two different answers.
Where New Drugs Come From Now
Although the spec's named drugs come from plants and microorganisms, most new drugs today are synthesised by chemists in the pharmaceutical industry.
Spec point
Most new drugs are synthesised by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted from a plant.
Three Spec Verbs — Don't Mix Them
The spec uses three different verbs deliberately. Digitalis and aspirin are extracted (originate from plants); penicillin was discovered (by Fleming, from a mould); modern drugs are synthesised (made by chemists). If a question asks how a drug was produced, match the verb to the source.
Watch
"Synthesised" means made in a lab from simpler chemicals. It does not mean extracted, purified, or grown. If a question contrasts traditional and modern drug discovery, the modern side is synthesis.
What Drugs Are Tested For
Before any new drug can be used to treat patients, it is extensively tested for three named properties. Mark schemes often award one mark per property.
1
Efficacy
2
Toxicity
3
Dose
PropertyWhat it asks
EfficacyDoes the drug actually work — does it treat the condition?
ToxicityIs it safe — does it cause harmful side effects?
DoseWhat amount produces the desired effect with the fewest side effects?
The Testing Pipeline
The spec splits testing into preclinical (in the lab) and clinical (in humans). The clinical stage itself has a low-dose start and an optimum-dose stage that may use placebos.
Preclinical Testing
Definition · Preclinical testing
Preclinical testing is done in a laboratory using cells, tissues and live animals. It happens before any human trial.
Spec wording is exact: "cells, tissues and live animals" — all three terms are credit-worthy in mark schemes. Don't substitute "human cells" or "people".
Why it has to come first
Preclinical work flags up early signs of toxicity and gives a rough dose range before any human is exposed. Skipping it is unsafe — and "tests on people first" is a classic wrong-answer in past-paper mark schemes.
Clinical Trials
Spec wording: "Clinical trials use healthy volunteers and patients."
Phase A — Healthy Volunteers
Very low doses of the drug are given at the start of the clinical trial. If the drug is found to be safe, the dose is gradually increased.
Phase B — Patients
Once safety is established, further clinical trials are carried out on patients with the condition to find the optimum dose.
Mark-Scheme Vocabulary
The exact phrase the spec uses for the right amount is "optimum dose". "Best dose" and "ideal dose" are usually accepted, but "optimum dose" is the safest wording to write.
Placebos & Double-Blind Trials
Definition · Placebo
A placebo is a substance given to some patients in a clinical trial that looks identical to the drug but contains no active ingredient.
Definition · Double-blind trial
A double-blind trial is one in which neither the patient nor the doctor knows whether the patient is receiving the real drug or the placebo, until after the results are analysed.
Why this matters
Placebos and blinding both exist for one reason: to remove bias. Patients who think they are getting the real drug may feel better just because of that expectation (the placebo effect). Doctors who know who is getting what may unconsciously rate patients differently.
Publication & Peer Review
The spec ties one skills-development point (WS 1.6) directly to this topic — and it's a recurring 1-mark item examiners ask about.
Spec point · WS 1.6
The results of drug testing and trials are published only after scrutiny by peer review.
What "peer review" means
Other scientists check the work before it is published. They look at the methods, the data and the conclusions to identify errors, bias, or unsupported claims. Only then can the results be released.
Why this matters
Peer review checks for honest mistakes and dishonest claims. Without it, a drug company could publish weak or selective results and persuade doctors to prescribe a drug that does not work — or is unsafe. The mark-scheme phrase to use is "checked by other scientists" or "scrutiny by peer review".
PEE Framework — Worked Example
Q. Explain why double-blind trials with placebos are used when testing a new drug. 3 MARKS
PPoint. Double-blind trials with placebos are used to remove bias from the results of a drug trial. EEvidence. Some patients are given the new drug; others are given a placebo — a substance identical in appearance but with no active ingredient. In a double-blind trial, neither the patient nor the doctor knows which group each patient is in. EExplain. Patients who know they have the real drug may feel better just from expectation (the placebo effect), and doctors who know who has which may unconsciously rate patients differently. Blinding both sides means any difference between the groups can be attributed to the drug itself, so the result is reliable.
Mark Scheme Chain
[1] placebo has no active ingredient · [1] neither patient nor doctor knows = double-blind · [1] removes bias / controls for the placebo effect.
Examiner Alerts
Alert 1 · Keep "willow" simple
For aspirin's source, the mark-scheme answer is the single word "willow". Mark schemes typically ignore named parts of willow (so "willow tree" or "willow bark" still score), but adding factually incorrect detail can cap the mark. Safest answer: just "willow".
Alert 2 · "Placebo" must name the property
Common mark-losers when defining a placebo: writing it is "a fake drug", or "the control", or "a substance that does nothing". None of these contain the mark-scheme requirement: "no active ingredient" (or equivalent — "inactive substance"). Use that exact phrasing.
Alert 3 · Three things, not one
Drugs are tested for efficacy, toxicity AND dose. The mark scheme typically awards one mark per property named. If asked "what are drugs tested for", listing only "safety" misses two marks.
Common Errors
✗ Wrong
"Aspirin comes from willow leaves."
✓ Right
"Aspirin originates from willow." (Keep it simple.)
✗ Wrong
"Drugs are tested on people first."
✓ Right
"Drugs are tested in the preclinical stage on cells, tissues, and live animals before any human trial."
✗ Wrong
"A placebo is the drug."
✓ Right
"A placebo contains no active ingredient; it is given to remove bias."
Practice Question
A new drug is being developed to treat a heart condition.
(a) Name one plant from which a traditional heart drug originates. 1 MARK
(b) Explain why the new drug must be tested on cells, tissues and live animals before being given to any human. 3 MARKS
a
Foxgloves — the named source of digitalis in the spec.
P
(b) Point. Testing on cells, tissues and live animals is the preclinical stage, used to check the drug for harmful effects before any human is exposed.
E
Evidence. At this stage, scientists test for toxicity (harmful effects), efficacy (does it work?) and a safe dose range.
E
Explain. If a drug were given to humans without this stage, unknown toxicity could cause serious harm. Preclinical testing means only drugs with a strong safety profile move into clinical trials, where very low doses are then given to healthy volunteers.
Recap — Three Takeaways
1
The three named drugs
Digitalis from foxgloves (heart drug) · Aspirin from willow (painkiller) · Penicillin from the Penicillium mould (antibiotic, discovered by Fleming).
2
Three properties drugs are tested for
Efficacy (does it work?) · Toxicity (is it safe?) · Dose (what is the optimum amount?).
3
The testing sequence
Preclinical (cells, tissues, live animals) → clinical with healthy volunteers (very low doses) → clinical with patients (find optimum dose; double-blind trials with placebos to remove bias).
Lesson 3.06 — Summary
In one sentence
Traditional drugs digitalis, aspirin and penicillin come from foxgloves, willow and Penicillium mould respectively; new drugs are tested for efficacy, toxicity and dose through preclinical work (cells, tissues, live animals) and then clinical trials (healthy volunteers at low dose, then patients with placebos in double-blind trials to remove bias).
TermHold-onto definition
Preclinical testingLab tests on cells, tissues and live animals .
Clinical trialDrug tested on healthy volunteers first, then patients .
PlaceboSubstance looking like the drug but with no active ingredient .
Double-blind trialNeither patient nor doctor knows who has the drug — removes bias .
Optimum doseDose that produces the desired effect with the fewest side effects.
Peer reviewOther scientists check the results before they are published (WS 1.6).
Next — Lesson 3.07
Coming up
Module 3 Masterclass — Infection & Response Synoptic 6-Markers. We bring together pathogens, defences and treatments to attack Level-3 extended-response questions on Paper 1.
Before you move on
Make sure you can recite the three drug–source pairs in under 10 seconds and list the three properties drugs are tested for. These are the cheapest marks in 4.3.1.9.
Next: The Marks That Get Thrown Away